231 
throughout the year, and it may be that some of the seasonal 
fluctuations in the chemical substances which have been dis- 
cussed in the preceding pages, and some of those in the plank- 
ton also, depend in some measure upon this changing effect of 
temperature upon the sewage. 
The following table, taken from Jordan (’00), gives the 
seasonal changes in numbers of colonies of bacteria from May 
BACTERIOLOGICAL EXAMINATION OF ILLINOIS RIVER AT HAVANA. 
Chlorine | 
‘ No. of colonies per cm*. 
Dae lt per mil, Stas of Temygatee| 
| lion) : | water, C. Havana Pekin 
May 30...... 13.6 8.7 21 4,500 542,000 
PUNECSG aes wy 13. 9.3 26 18,450 129,000 
13 3e-). 0s 13.5 8.8 25 15,900 205,000 
ZO Wasser 12.1 a5 26 2,500 225,000 (1) 
28 ates 14.9 5.2 25 4,500 2,030,000 (2) 
July 85socns 14.7 4.7 26 2,400 52,000 (3) 
D2eaciea 23. 4.1 26 7,300 1,435,000 
Sisgncos 36. 4.9 27 5,700 470,000 (4) 
200 en. 31. 4.8 30 850 980,000 (5) 
PIES OQ ee ces 27.5 4.1 26 1,550 985,000 (6) 
3 peters 34. 3. 26 goo 10,000 (7) 
80h ts 30. ray 29 9,800 30,000 (8) 
Sept, (Osesco. 40. 2.4 2 1,900 650,000 (9) 
NAV yaretele 46. 2.5 22 1,500 310,000 (10) 
ZO Fs.ccis= 35. 3.5 14 3,400 240,000 (It) 
2 Mic ieeye 49. 3- 16 3,700 120,000 (12) 
OCU, Was aches 52. 3. 14.5 2,500 | 500,000 (13) 
Ieee 50. 3.2 16. 6,600 | 430,000 (14) 
Toceeece 58. 3.2 17. 8,800 
BE ewes 60.5 3. 12. 3,900 30,000 (15) 
INOVeonloace ox 63. 3.5 9. 7,000 150,000 (16) 
Thiers SI. 3.7 10 »300 =| ~~ 30,000 
Dea Feysis« 47.5 4.4 II 128,000 ~—|_ 1,650,000 
Zarate ts 43. my 41,600 | 380,000 (17) 
Decy §Onsccts sty Bit wh 85,000 | 140,000 (18) 
DON een 35 4.8 I | 66,800 | 5,000 
(1) June 21. (2) June 27. (3) July 6. (4) July 18. (5) July 25. (6) Aug. 8. (7) 
Aug. 22. (8) Aug. 29. (9) Sept.5. (10) Sept. 12. (11) Sept. 18. (12) Sept. 26. (13) 
Oct. 3. (14) Oct. 10. (15) Oct. 31. (16) Nov. 7. (17) Nov. 30. (18) Dec. 5. 
30, 1899, till the end of the year at Havana, and at Pekin, 
thirty-two miles above. The decline from the larger numbers 
in June to a fairly well-maintained minimum during midsum- 
mer at Havana is very evident, as is also the rise as the tem- 
perature lowersinthe autumn. Both the period of time andthe 
